This section provides background information related to the present disclosure which is not necessarily prior art.
Traditionally, engine components for automotive applications have been made of metals, such as steel and iron. Metals components are robust, typically having good ductility, durability, strength and impact resistance. While metals have performed as acceptable engine components, they have a distinct disadvantage in being heavy and reducing gravimetric efficiency, performance and power of a vehicle thereby reducing fuel economy of the vehicle.
Weight reduction for increased fuel economy in vehicles has spurred the use of various lightweight metal components, such as aluminum and magnesium alloys as well as use of light-weight reinforced composite materials. While use of such lightweight materials can serve to reduce overall weight and generally may improve fuel efficiency, issues can arise when using such materials in an engine assembly due to high operating temperatures associated with the engine assembly. For example, the lightweight metal components can also have relatively high linear coefficients of thermal expansion, as compared to traditional steel or ceramic materials. In engine assemblies, the use of such lightweight metals can cause uneven thermal expansion under certain thermal operating conditions relative to adjacent components having lower linear coefficients of thermal expansion, like steel or ceramic materials, resulting in separation of components and decreased performance. Additionally, lightweight reinforced composite materials may have strength limitations, such as diminished tensile strength, and they can degrade after continuous exposure to high temperatures. Thus, lightweight engine assemblies having increased durability under high temperature operating conditions along with enhanced methods of heat transfer (e.g., heating and cooling) for such engine assemblies are needed to further improve efficiency of operation and fuel economy. However, manufacturing such lightweight engine assemblies which have a combination of lightweight materials and traditional materials can be challenging, particularly, with respect to fastening polymeric composite components with metal components.
Typically, primary engine assembly components, such as a cylinder head, cylinder housing, and crank housing, are joined together via a plurality of threaded metal fasteners (e.g., bolts). However, use of such traditional threaded metal fasteners can prove problematic when one or more of the engine components comprises a polymeric composite material. More specifically, the polymeric composite material usually comprises an arrangement of fibers and forming a channel, particularly a threaded channel, for receiving at least one of the threaded metal fastener can cause the fibers to break and/or fray in the polymeric composite resulting in compromised structural integrity of the polymeric composite component. Additionally, traditional metal fasteners and polymeric composite components when used together can undergo uneven thermal expansion under certain thermal operating conditions due to the difference in linear coefficients of thermal expansion between the materials. As known in the art, uneven thermal expansion can cause spin loss and thus diminish performance and fuel efficiency of the engine assembly. Therefore, methods of joining a combination of material components, particularly polymeric composite components, to form lightweight engine assemblies without diminishing structural integrity of the components are needed.